Linux Ethernet Bridging - Feb 2018 - [Bridge] [PATCH net] bridge: Fix VLAN reference count problem

When a VLAN is added on a port, a reference is taken on the
corresponding master VLAN entry. If it does not already exist, then it
is created and a reference taken.

However, in the second case a reference is not really taken when
CONFIG_REFCOUNT_FULL is enabled as refcount_inc() is replaced by
refcount_inc_not_zero().

Fix this by using refcount_set() on a newly created master VLAN entry.

Fixes: 251277598596 ("net, bridge: convert net_bridge_vlan.refcnt from
atomic_t to refcount_t")
Signed-off-by: Ido Schimmel <idosch at mellanox.com>
---
 net/bridge/br_vlan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
index 51935270c651..9896f4975353 100644
--- a/net/bridge/br_vlan.c
+++ b/net/bridge/br_vlan.c
@@ -168,6 +168,8 @@ static struct net_bridge_vlan *br_vlan_get_master(struct
net_bridge *br, u16 vid
 		masterv = br_vlan_find(vg, vid);
 		if (WARN_ON(!masterv))
 			return NULL;
+		refcount_set(&masterv->refcnt, 1);
+		return masterv;
 	}
 	refcount_inc(&masterv->refcnt);
 
-- 
2.14.3

On 25/02/18 21:59, Ido Schimmel wrote:
> When a VLAN is added on a port, a reference is taken on the
> corresponding master VLAN entry. If it does not already exist, then it
> is created and a reference taken.
> 
> However, in the second case a reference is not really taken when
> CONFIG_REFCOUNT_FULL is enabled as refcount_inc() is replaced by
> refcount_inc_not_zero().
> 
> Fix this by using refcount_set() on a newly created master VLAN entry.
> 
> Fixes: 251277598596 ("net, bridge: convert net_bridge_vlan.refcnt from
atomic_t to refcount_t")
> Signed-off-by: Ido Schimmel <idosch at mellanox.com>
> ---
>  net/bridge/br_vlan.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> index 51935270c651..9896f4975353 100644
> --- a/net/bridge/br_vlan.c
> +++ b/net/bridge/br_vlan.c
> @@ -168,6 +168,8 @@ static struct net_bridge_vlan
*br_vlan_get_master(struct net_bridge *br, u16 vid
>  		masterv = br_vlan_find(vg, vid);
>  		if (WARN_ON(!masterv))
>  			return NULL;
> +		refcount_set(&masterv->refcnt, 1);
> +		return masterv;
>  	}
>  	refcount_inc(&masterv->refcnt);
>  
> 
Good catch,

Acked-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>

From: Ido Schimmel <idosch at mellanox.com>
Date: Sun, 25 Feb 2018 21:59:06 +0200
> When a VLAN is added on a port, a reference is taken on the
> corresponding master VLAN entry. If it does not already exist, then it
> is created and a reference taken.
> 
> However, in the second case a reference is not really taken when
> CONFIG_REFCOUNT_FULL is enabled as refcount_inc() is replaced by
> refcount_inc_not_zero().
> 
> Fix this by using refcount_set() on a newly created master VLAN entry.
> 
> Fixes: 251277598596 ("net, bridge: convert net_bridge_vlan.refcnt from
atomic_t to refcount_t")
> Signed-off-by: Ido Schimmel <idosch at mellanox.com>
Applied and queued up for -stable, thanks!